What is the role of protein in a cell?

Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body's tissues and organs. These proteins provide structure and support for cells. On a larger scale, they also allow the body to move.

Explanation:

three major roles of proteins are:

hormones. Many hormones are protein in nature; hormones control growth and metabolic activities of the body.

catalytic activities. Enzymes are globular protein.  

Transport of oxygen.

Blood Clotting.

Immunity.

Muscles contractility.

idk why hjggjhjkhj

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.